Research On Microstructure And Properties Of Magnesium Alloy Strengthened By Ultrasonic Shot Peening Combined With Laser Shock Peening

Magnesium alloy is a widely used lightweight engineering material,but its poor wear resistance and corrosion resistance are the main reasons limiting its large-scale application.Laser shock peening(LSP)and ultrasonic shot peening(USP)are two surface strengthening technologies used to improve the properties of magnesium alloys.However,the single use of the above two technologies can no longer meet severe working requirements of magnesium alloys.To achieve better surface performance of AZ31 B magnesium alloy,this paper combines the two technologies of USP and LSP,and verifies the composite strengthening process through surface integrity testing,friction wear,electrochemical corrosion and full immersion corrosion experiments.The main research and results are as follows:Theoretical basis of ultrasonic shot peening combined with laser shock peening strengthening.Based on the residual stress,redistribution and grain refinement behaviour of USP and LSP,the strengthening mechanisms of USP and LSP on the surface properties of magnesium alloy were investigated.Surface integrity of magnesium alloy strengthened by USP combined with LSP.The surface morphology,hardness,residual stress and microstructure of the strengthened magnesium alloy were analyzed using confocal microscopy,Vickers hardness tester,X-ray diffractometer and optical microscope.The results show that compared with USP,the surface roughness of magnesium alloy after composite strengthening decreases,while the amplitude an depth of compressive residual stress increases.The surface microhardness of magnesium alloy after composite strengthening reaches 118 HV(40% higher than that of LSP)and the depth of hardened layer is 1.0 mm(0.4 mm deeper than that of LSP).The wear resistance of magnesium alloy strengthened by USP combined with LSP.The friction and wear properties of magnesium alloy after USP,LSP and USP+LSP were investigated.The experimental results show that the compressive residual stress introduced by the three methods can suppress the initiation and propagation of fatigue cracks during friction,which contributes to the improvement of the wear resistance of magnesium alloys.The wear mechanisms of as received sample are fatigue wear and abrasive wear,while for surface strengthened sample,the wear mechanisms are oxidation wear and abrasive wear accompanied by adhesive wear.Compared with USP and LSP,the USP+LSP process introduces a larger and deeper compressive residual stress,which contribute to better wear-resistant performance.The corrosion resistance of magnesium alloy strengthened by USP combined with LSP.Through full immersion corrosion and electrochemical corrosion experiments,the corrosion behaviours of magnesium alloy after USP,LSP and USP+LSP were investigated.The results show that the grain refinement and compressive residual stress layer induced by USP and LSP on the surface of magnesium alloy contribute to the improvement of the open circuit potential and self-corrosion current,the reduction of corrosion current,the increasement of impedance spectral radius and charge transfer resistance.Therefore,the amount of evolved hydrogen and corrosion rate decreased after USP,LSP and USP+LSP.The USP+LSP introduces larger and deeper compressive residual stress as well as a higher degree of grain refinement,resulting in superior corrosion resistance.